The Administrative Core (Core A) will serve as a centralized facility designed to manage all operations related to this PP and facilitate the interactions between the collaborating laboratories. The major tasks of this Core component will be to: a) communicate the central scientific theme to which all component projects will direct their research efforts; b) manage the fiscal aspects of the PP, maintain financial records and other administrative functions; and (c) promptly and properly distribute or coordinate the distribution of materials (chemicals, biologicals, ligands, radioligands, receptor mutants, antibodies, clones, etc.) produced under the auspices of Core B and the other projects. The Administrative Core will also take responsibility for synchronizing the operations and communications between the individual laboratories involved in the PP and other laboratories which interact collaboratively at no cost to the project. This effort will include recording and distributing materials produced to the participant laboratories and to the collaborating laboratories, together with maintaining and updating the data base related to this collaborative effort. Additional specific coordinating efforts will include regular telephone conferences, the yearly group meeting of participants and collaborators, as well as other communications, including the maintenance of a Web page dedicated to Program Project activities. The quarterly meetings with the Internal Advisory Committee, as well as the yearly formal meeting with the External Scientific Advisory Committee, will also be organized under Core A. The Administrative Core will maintain or increase the common or shared resources that are required for the performance of the inter-related tasks for the component research projects. General administrative support related to this Program Project, including financial management, correspondence, and preparation of reports and proposals, will also be provided by this Core Facility. The Core A proposal also includes a brief summary of all of the Program Project components and an outline of the scientific interactions between the participating laboratories, including lines of authority, program coordination and evaluation. The synergistic aspect of the different collaborations, all working in this specialized area of mutual scientific and public health interest, constitutes a major strength of this unique multidisciplinary research effort.